Agentcad Skill

CAD tool for AI agents. Use when the user asks you to design, model, or build a 3D object. agentcad executes build123d or CadQuery Python scripts and produces STEP files, PNG renders, mesh exports (STL/GLB/OBJ), and geometric metrics.

agentcad — CAD tool for AI agents

You have access to agentcad, a CLI that turns build123d or CadQuery Python scripts into 3D geometry. All output is JSON. Every command returns "command" and "status" keys.

First-time setup

bash

agentcad init --name <project_name>
agentcad --help   # Read this — it is your complete operational briefing

Core workflow

1. Write a script. No imports needed — build123d primitives, show_object, and agentcad edit helpers are pre-injected by default. show_object(result) is required.

2. Dry-run first to check metrics without consuming a version:

   bash

   agentcad run script.py --output test --dry-run
   

   Check volume, dimensions, is_valid in the response.

3. Run for real. Visual feedback is on by default:

   bash

   agentcad run script.py --output label
   

   Every successful run produces (paths in the JSON response):

   • preview.png — 4-view composite (front, right, top, iso). Read this to confirm the part looks right before iterating. One image, all 4 angles.
   • diff.side_by_side — side-by-side PNG vs the most recent successful prior version. Read this when iterating to see what your change did.
   • diff.overlay — tinted (green prev, red this) overlay for subtle shifts. Read only if side-by-side didn't resolve the question.
   • viewer.html — interactive 3D viewer for the user (humans only; you can't render HTML). Mention it to the user so they open it.

   Pass --no-preview only for tight parametric sweeps where latency matters.

4. Show the user. After a successful build, open the interactive viewer:

   bash

   agentcad view v1_label/viewer.html   # or output.step / output.glb
   

   Users expect to see the result in a browser. Do this every run, unprompted.

5. Inspect if invalid. If is_valid: false or geometry looks wrong:

   bash

   agentcad inspect v1_label/output.step
   

6. Iterate. Fix the script, run with a new --output label. Use agentcad diff 1 2 to compare versions.

Script writing rules

• show_object(result) is required — at least one call.
• These are pre-injected by default (no import needed): build123d primitives like Box, Cylinder, Sphere, Plane, plus show_object, load_step, pick_face, pick_edge, fillet_edges, chamfer_edges, shell_faces, cut_pocket, boss, split_by_plane, and replace_face.
• CadQuery remains supported. Use import cadquery as cq, initialize with agentcad init --runtime cadquery, or pass --runtime cadquery.
• CadQuery helper paths operate on TopoDS_Shape. Bridge with .val().wrapped:

  python

  import cadquery as cq
  part = cq.Workplane('XY').box(10, 20, 5).val().wrapped
  moved = translate(part, 50, 0, 0)
  

• To show helper output:

  python

  import cadquery as cq
  show_object(cq.Workplane('XY').newObject([cq.Shape.cast(topo_shape)]))
  

• For OCP internals (gp_Pnt, BRepPrimAPI, etc.), import manually.

Key commands

Command	Purpose
agentcad init --name NAME	Initialize project
agentcad run SCRIPT --output LABEL	Execute script, produce STEP + metrics
agentcad run ... --dry-run	Metrics only, no version consumed
agentcad run ... --no-preview	Suppress preview (on by default)
agentcad run ... --render iso,front	PNG views
agentcad run ... --export stl,glb	Mesh export
agentcad run ... --params k=v,k=v	Override script parameters
agentcad render STEP --view SPEC	Post-hoc renders with camera control
agentcad export STEP --format stl,glb	Post-hoc mesh export
agentcad inspect STEP	Topology report (validity, free edges)
agentcad diff REF1 REF2	Compare versions
agentcad context	Project state
agentcad docs [SECTION]	Deep-dive docs (16 sections)
agentcad view FILE	Run this after every successful build — opens GLB/STEP in the user's browser

Debugging playbook

1. Check metrics first — volume and dimensions catch most issues.
2. Read preview.png — the 4-view composite. Fastest way to spot obvious problems.
3. Read diff.side_by_side if iterating — confirms your change did what you intended.
4. Negative volume? Wire winding is backwards (CW instead of CCW).
5. is_valid: false? Run agentcad inspect — check free_edge_count and shell status.
6. Hollow shape? free_edge_count > 0 means open shell.
7. Complex profiles (gears, splines)? Use subtractive construction — cut from a blank cylinder/box instead of building up. See agentcad docs patterns.

Patterns

• Build at origin, then position: Create geometry at origin, use translate() and rotate() to place it.
• Compound vs Union: makeCompound() for assemblies (parts stay separate), .union() for boolean fuse into one solid.
• Parametric scripts: Top-level variable assignments become overridable via --params. Use this for iteration.
• Named parts: show_object(shape, name="wheel", options={"color": "red"}) for per-part metrics and colored GLB export.